PULSE 53: Pelagic-Benthic Coupling and the Carbon Cycle
September 17 - September 23 , 2007

September 21, 2007

Mike Vardaro and Jim Birch write:
benthic roverOur 5th day at sea finds everyone settling into a routine; we all know the science work that needs to be accomplished, when and where the food is, how to stay out of the way when the crew needs to launch or recover the ROV, and very important, how to take a shower when the shower-stall is constantly rocking back and forth.

On Friday we awoke early and the pilots deployed the ROV. To send this robot down to 4000 meters takes almost 2 hours, so there is much waiting until it reaches the bottom. About an hour after launching the ROV, we sent the Benthic Rover over the side. This is a vehicle with treads like a bulldozer that roams around the seafloor measuring oxygen uptake by creatures and bacteria living in the sediment. By understanding how much oxygen is being used by organisms in the seafloor sediment, we can estimate how many organisms there are in that area, how active they are, and how that changes over time in response to seasonal and interannual changes in food supply. These are important for understanding the connections between the surface and the seafloor, the energy needs of deep-sea animals, and how deep-sea biological populations react to the changing ratio between the food supply and their energy demands.

The trick with the Rover is that it is completely autonomous, with no connection to the surface. All of its instructions are programmed into its 'brain', a titanium sphere about the size of a basketball filled with electronics. These instructions tell the Rover where to turn, how long to drive, when to put down the respiration chambers into the sediment, and when to remove and clean the chambers, and move to the next pre-programmed site. The Rover is slightly positively bouyant, so carries with it a 93 kg (250 lb) drop weight that helps it stay on the bottom. In fact, the Rover weighs around 950 kg or 2500 lbs in the air, but when placed in the water it weighs only 56 kg (150 lbs). Thus, when commanded to release the drop weight, the Rover becomes positively bouyant by 37 kg or 100 lbs (56 lg rover wt - 93 kg drop weight = -37 kg) and slowly floats to the surface.

Yesterday, after the ROV reached the bottom, we waited for the Rover to land. When it did, we flew over and watched the Rover run through some of its check-out routines, then left it for a 3-day mission. We will return on Sunday to retrieve the Rover and its data.

The rest of the day was spent flying the ROV along a transect to record the numbers and positions of the animals that were visible. Videotape analysis of this flight will allow estimation of population densities and species diversity. Several biological and sediment samples were also collected for various studies (such as one on the life history and genetics of deep-sea sponges made of siliceous spicules – basically glass fibers! – and one on sea urchin bioturbation).

Even though tomorrow is Saturday, we have a full day of science planned – since cruises such as this are so expensive and scientifically valuable, there is no time to take days off!

Have a good weekend,

Jim and Mike

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